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Preparation of salt buffers

点击： 作者：51protocol收集 来源： 时间： 2007-03-13 　本站论坛

Centrifuge the sample through a 0.45 mm filter.

Check the absorbance at 260 nm and, if necessary, dilute the sample down to a concentration that will not exceed the capacity of the column (Dionex NucleoPac™ 9 ´ 250 PA-100; P/N 43011 (anion exchange) column listed bel ow). Typically a 1 ml injection loop is used to inject a 10 mM sample of unlabeled dNTPs Cy-dUTP.

HPLC Purification
Column used: Dionex NucleoPac™ 9 ´ 250 PA-100; P/N 43011 (anion exchange)
HPLC Equipment: Perkins Elmer Series 200 LC Pump, Perkins Elmer UV/Vis Detector LC 295

1. Equilibrate column in buffer system, 3 mL/min flow rate (general purge method)
1.1. 5 min low salt buffer (LSB) or A
1.2. 2 min gradient to 100% high salt buffer (HSB) or B
1.3. 5 min HSB or B
1.4. 2 min gradient to 60% LSB or A
1.5. 5 min 60% LSB or A

2. Load sample into injection loop. See "Final Considerations" on the next page for sample lot size and other issues.

3. Run gradient (3 mL/min flow, chart recorder 0.5 cm/min)
3.1. 5 min 60% LSB, 40% HSB
3.2. 10 min gradient to 80% HSB
3.3. 1 min gradient to 100% HSB
3.4. 10 min 100% HSB
3.5. 1 min gradient to 60% LSB
3.6. 5 min 60% LSB

Final Preparative Procedures
For a preparative run of 150 nmoles Cy-dUTP (note "Final Considerations"), the recovered fractions of purified Cy-dUTP is eluted in 5 ml of volatile TEAA buffer that can be removed by lyophilization.
Lyophilization and Redilution
(Return to HPLC Preparation.)

Pool fractions of each Cy dye into a 50 mL conical tube. Punch holes into the cap using an 18-gauge needle. Avoid exceeding more than half the volume of the tube, as the samples may have a tendency to splatter during degassing or travel up the tube during lyophilization.

Freeze the samples on dry ice and transfer them to a lyophilization chamber. Wrap the chamber with foil to protect the samples from light.

Lyophilize the samples to completion (approx. 12-15 hrs for HPLC-purified samples, 6-10 hrs for Sep-Pak-purified material). HPLC-purified samples will have the appearance of a residue until most of the TEAA is removed.
Note: Steps 4 & 5 are for HPLC-purified samples only.

Dilute the samples back up to 8-10 mL with 0.22 mm filtered ddH₂O and lyophilize until the samples again resemble residue. This time, it may require up to 24 hours of lyophilization.

Repeat Step 4. Lyophilization is complete when the sample has the appearance of a film and/or specks of solid residue. Resuspend the sample in a small volume of 10 mM phosphate buffer, pH 7.0. Bear in mind that some of the Cy-dUTP will coat the upp er regions of the tube walls and may not be readily visible. Check absorbance of the sample. A_560/660/A₂₆₀ratios should be around 17 for cy 3 and 25 for cy 5.

Expected overall yields: cy 3: 50-70%; cy 5: 45-65%.

Final Considerations

Currently 150nmol of Cy-dUTP contained in a 10 mM mixture of labeled and unlabeled dNTPs is loaded onto the column listed above, depending on the contents and concentration of the filtrate; PCR flow-through samples tend to be cleaner and may allow for larger injection lots. Thus, the flow-through from PCR and RT reactions may be kept separate so that they can be processed separately. The Sep-Pak purification desalts the sample and is likely to remove other impurities present in the sample. HPLC purif ication can still be performed without Sep-Pak purification, but salt content prohibits injection of more than 50nmol. Furthermore, yields tend to be lower if the sample is not desalted prior to HPLC injection.

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